The present invention relates to hydrocarbon soluble molybdenum complexes of thio-bis-phenols, their method of preparation and their utility as an additive for hydrocarbon compositions such as gasoline, fuel oil and lubricating oils including greases, industrial oils, gear oils and lubricants for engines and other equipment having moving parts operating under boundary lubricating conditions.
There are many instances, as is well known, particularly under "Boundary Lubrication" conditions where two rubbing surfaces must be lubricated, or otherwise protected, so as to prevent wear and to insure continued movement. Moreover, where, as in most cases, friction between the two surfaces will increase the power required to effect movement and where the movement is an integral part of an energy conversion system, it is most desirable to effect the lubrication in a manner which will minimize this friction. As is also well known, both wear and friction can be reduced, with various degrees of success, through the addition of a suitable additive or combination thereof, to a natural or synthetic lubricant. Similarly, continued movement can be insured, again with varying degrees of success, through the addition of one or more appropriate additives.
While there are many known additives which may be classified as antiwear, antifriction and extreme pressure agents and some may in fact satisfy more than one of these functions as well as provide other useful functions, it is also known that many of these additives act in a different physical or chemical manner and often compete with one another, e.g. they may compete for the surface of the moving metal parts which are subjected to lubrication. Accordingly, extreme care must be exercised in the selection of these additives to insure compatibility and effectiveness.
The metal dihydrocarbyl dithiophosphates are one of the additives which are known to exhibit antioxidant and antiwear properties. The most commonly used additives of this class are the zinc dialkyl dithiophosphates which are conventionally used in lubricant compositions. While such zinc compounds afford excellent oxidation resistances and exhibit superior antiwear properties, it has heretofore been believed that the same increases or significantly limits the ability to decrease friction between moving surfaces. As a result, compositions containing zinc dialkyl dithiophosphates were not believed to provide the most desirable lubricity and, in turn, it was believed that use of compositions containing the same would lead to significant energy losses in overcoming friction even when antifriction agents are included in the composition.
Known ways to solve the problem of energy losses due to high friction, e.g. in crankcase motor oils include the use of synthetic ester base oils which are expensive and the use of insoluble molybdenum sulfides which have the disadvantage of giving the oil composition a black or hazy appearance.
U.S. Pat. No. 3,047,500 is concerned with oil-soluble extreme pressure agents which are prepared from molybdenum pentachloride and an oil-soluble alkyl phenol, for instance a polyalkyl or dialkyl phenol containing a total of at least 6 carbon atoms in the side chain (col. 2, lines 15-20). Although the specification does not disclose or mention thio-bisphenols, it does teach that the molybdenum phenolate can be used in combination with an oil-soluble organic sulfur compound in the lubricating oil such as sulfurized sperm oil (see col. 3, lines 10-54 and Table I of col. 4).
U.S. Pat. No. 3,541,014 is concerned with oil-soluble molybdenum complexes prepared from molybdenum-containing anions and assorted overbased materials. The promoters for the preparation of these molybdenum complexes include mono- and dialkylated phenols which appear to be retained in the overbased mixture (see col. 5, lines 58-67).
Other types of molybdenum compounds taught to be useful in lubricating oils include the alkyl esters of molybdic acid as corrosion inhibitors (see U.S. Pat. No. 2,805,997) which appear to be hydrolytically unstable and nitrogenous thiomolybdates as metal antiwear additives which are said to function by providing a coating of reduced coefficient of friction (see U.S. Pat. No. 2,938,869). Chloromolybdenum esters of phenols are taught to be useful as extreme pressure additives for lubricants (U.S. Pat. No. 3,047,506) although the presence of chlorine can be a cause of corrosion in crankcase lubricants. Another extreme pressure additive is taught in the form of an oil-soluble molybdenum complex produced by the displacement of carbonate from an overbased metal detergent with a molybdenum-containing anion (U.S. Pat. No. 3,541,014).
Similarly, antifriction agents or oiliness or lubricity agents as the same are often referred to in the prior art, function by forming a coating on the surface of the moving metal parts. As in the case of antiwear agents, however, the coating bonds are, generally, effected physically, rather than chemically, and, indeed, the bonding between an antifriction agent and the surface is, generally weaker than the bond formed between an antiwear agent and the metal surface.
In light of the foregoing, the need for improved lubricating compositions that will permit operation of moving parts under boundary conditions with reduced friction is believed to be readily apparent. Similarly, the need for such a composition that can include conventional base oils and other conventional additives and can be used without the loss of other desirable lubricant properties, particularly those provided by zinc dialkyl dithiophosphates, is also readily apparent.